New Standards for Wireless LANs

New Standards for 

Wireless LANs 

Summer Term 2011 

Dr.-Ing. Andreas Könsgen 

Dr.-Ing. Koojana Kuladinithi 

TZI-ikom – University of Bremen 

E-Mail: {ajk|koo}@comnets.uni-bremen.de 

Phone: (0421) 218 62380 

www.comnets.uni-bremen.de/~ajk 

Room S2310 (NW1)

Acknowledgement 

This lecture is based on material by 

Prof. Dr.-Ing. Andreas Timm-Giel 

Institute of Communication Networks 

Technical University of Hamburg-Harburg 

Germany 

- 2 - 

TZI – FB 1 – Kommunikationsnetze 

Andreas Könsgen – Summer Term 2011

Exam: 

Organisational Issues 

• Oral Exam (30min) after the end of the term 

Questions, Critics etc.: 

• always welcome 

How to reach me? 

• In my office S2310, or send an e-mail 

Exercises: 

• After the lecture, S 1270, 11:00 to 11:45 

• deepen understanding, open discussion, some 

labs/demos/simulation 

• Slides available on www.comnets.uni-bremen.de 

under “WLAN course” 

- 3 - 



No lecture/tutorial: 

Organisational Issues 

• 25 April because of Easter holidays 

• 13 June because of public holiday 

– Will be taken at some other date 

– To be fixed later 

- 4 - 



Objective of the Lecture 

● Understand wireless technologies: how do 

they work? 

● Give an overview on existing and emerging 

wireless standards 

● Give an idea what is coming up in the 

future in Wireless Communications 

- 5 - 



Overview: 

Course Overview (1) 

● Mobile and Wireless Communications Basics 

― radio propagation 

― Modulation and coding 

― multiple access, duplex schemes, access protocols 

● IEEE 802.11(Wireless LAN) 

— Overview 802.11 a, b, g, h... 

— Physical Layer 

— MAC Layer 

— Security 

- 6 - 



Course Overview (2) 

● IEEE 802.16 – Wireless Metropolitan Area Network 

(WMAN) – WiMAX 

● IEEE 802.20 – Mobile Broadband Wireless Access 

(MBWA) 

● IEEE 802.15 – Wireless Personal Area Network 

(WPAN): Bluetooth and Zigbee 

● Sensor Networks (Dr. Koojana Kuladinithi) 

- 7 - 



Literature 

• See Website – www.comnets.uni-bremen.de 

• Jochen Schiller – Mobilkommunikation, Pearson, 2003, 

available in English, from Addison-Wesley. 

• James F. Kurose, Keith W. Ross, Computer Networking – A top- 

Down Approach, 4 th Edition, 2008, Pearson International 

Edition 

• Bernhard H. Walke – Mobile Radio Networks, J. Wiley & Sons, 

1999 

• Walke, UMTS – the fundamentals 

• IEEE Standardisation documents (links on website) 

• Many others, like: 

– K. David/T. Benkner, Digitale Mobilfunksysteme, Teubner, 

1996 

– Kammeyer, Nachrichtenübertragung, Teubner, 1996 

- 8 - 



Chapter 1: First Mobile and 

Wireless Communication 

Systems

Definition of Wireless and Mobile 

• Wireless 

– Communication without wires, can be 

mobile and fixed 

• Mobile 

– Portable devices (laptops, notebooks etc.) 

connected at different location to wired 

networks (e.g. LAN or PSTN) 

– Portable devices (phones, notebooks, 

PDAs etc.) connected to wireless networks 

(UMTS, GSM, WLAN….) 

- 10 - 



Early History of Wireless Communications 

• In history first light and sound have been used to transmit 

messages over wide distances 

- 11 - 

Pics from http://www.connected-earth.com 



Transmission of Electromagnetic Waves 

• 1831: Faraday demonstrates 

magnetic induction 

• 1865: Maxwell theory of 

electromagnetic fields, wave 

equation 

• 1876 Patent on phone, Alexander 

Graham Bell (Antonio Meucci 1849) 

• 1888: H. Hertz: demonstrates 

the wave character of electrical 

transmission through space 

• Nikola Tesla extends the 

transmission range 

Pics from www.wikipedia.org 

- 12 - 



History of Wireless Communication 

• 1895 Guglielmo Marconi 

– first demonstration of wireless 

telegraphy (digital!) 

– 1901 transatlantic transmission 

– long wave transmission, high 

transmission power necessary (> 200kW) 

• 1907 Commercial transatlantic connections 

– huge base stations 

(30 100m high antennas) 

• 1915 Wireless voice transmission New York - San Francisco 

• 1920 Discovery of short waves by Marconi 

– reflection at the ionosphere 

- 13 - 

Foto from www.wikipedia.org 

– smaller sender and receiver, possible due to the invention of the 

vacuum tube (1906, Lee DeForest and Robert von Lieben) 



1924 

Beginning of Mobile Communications 

• 1911 mobile transmitter on Zeppelin 

• 1926 train (Hamburg – Berlin) 

• 1927 first commercial car radio (receive only) 

• First Mobile Communication Systems started 

in the 40s in the US and in the 50s in Europe. 

- 14 - 

CONCEPTS: 

• Large Areas per 

Transmitter 

• „Mobiles“ large, high 

power consumption 

• Systems low capacity, 

interference-prone 

• Expensive !!! 



Today's Wireless Communication (1) 

1984 CT-1 standard (Europe) for cordless telephones 

– In Germany selling no longer permitted since 2009 

1992 DECT 

– Digital European Cordless Telephone (today: Digital 

Enhanced Cordless Telecommunications) 

– 1880-1900MHz, ~100-500m range, 120 duplex channels, 

1.2Mbit/s data transmission, voice encryption, 

authentication, up to several 10000 user/km 2 , used in 

more than 50 countries 

1996 HiperLAN (High Performance Radio Local Area 

Network) 

– ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s 

– recommendations for type 2 and 3 (both 5GHz) and 4 

(17GHz) as wireless ATM-networks (up to 155Mbit/s) 

– Did not enter market 

- 15 - 



Today's Wireless Communications (2) 

In the 1990s: many proprietary products for wireless 

networks 

1997 Wireless LAN – IEEE standard 802.11 

2.4-2.5 GHz and infrared, 2Mbit/s 

1999 IEEE 802.11b, 2.4 GHz, 11Mbit/s 

1999 IEEE 802.11a, 5 GHz, 54 Mbit/s 

1999/2001 Bluetooth/IEEE 802.15.1 for piconets, 

2.4 GHz, < 1Mbit/s 

2003 IEEE 802.11g, 2.4 GHz, 54 Mbit/s 

2003/2004 Zigbee/IEEE 802.15.4 for sensor networks 

2009 IEEE 802.11n, 2.4 and 5 GHz, 600 Mbit/s 

- 16 - 



End Chapter 1

Chapter 2 – Mobile 

Communications 

Definitions & Basics

Chapter 2 - Overview 

• Part 1 (today) 

– Digital Transmission System 

– Frequencies, Spectrum Allocation 

– Radio Propagation and Radio Channels 

• Part 2 (next week) 

– Modulation, Coding, Error Correction 

• Part 3 (in 2 weeks) 

– Capacity limits 

– Duplexing schemes 

– Media Access Protocols 

- 19 - 



Acknowledgement 

• Pictures and some slides of this chapter are 

taken from: 

– B. Walke, P. Seidenberg, M. P. Althof, 

UMTS: the fundamentals, Wiley 

– Schiller: Mobilkommunikation (Mobile 

Communications), Pearson 

Studium/Addison Wesley, 2003/2002 

– David/Benkner: Digitale 

Mobilfunksysteme, Teubner 1996 

– Proakis/Saleh, Grundlagen der 

Kommunikationstechnik, Pearson Studium 

2004 

- 20 - 



Application 

Transport 

Network 

Data Link 

Physical 

Simple Reference Model 

Radio 

Network Network 

Data Link 

Physical 

Data Link 

Physical 

- 21 - 

Wired Medium 

Application 

Transport 

Network 

Data Link 

Physical 



More Detailed Reference Model 

• Application layer 

• Transport layer 

• Network layer 

• Data link layer 

• Physical layer 

– service location 

– new applications, multimedia 

– adaptive applications 

– congestion and flow control 

– quality of service 

– addressing, routing, 

device location 

– Hand-over 

– authentication 

– media access 

– multiplexing 

– media access control 

– encryption 

– modulation 

– interference 

– attenuation 

– frequency 

- 22 - 



Structure of Digital Transmission System 

Digital Source 

Sink 

- 23 - 



twisted 

pair 

1000 km 

300 Hz 

Frequencies for Communication 

10 km 

30 kHz 

coax cable 

100 m 

3 MHz 

VLF LF MF HF VHF UHF SHF EHF infrared visible 

light 

UV 

VLF = Very Low Frequency UHF = Ultra High Frequency 

LF = Low Frequency SHF = Super High Frequency 

MF = Medium Frequency EHF = Extra High Frequency 

HF = High Frequency UV = Ultraviolet Light 

VHF = Very High Frequency 

Frequency and wave length: 

λ = c /f 

1 m 

300 MHz 

With wave length λ, speed of light c ≈ 310 8 m/s, frequency f 

- 24 - 

10 mm 

30 GHz 

100 μm 

3 THz 

optical transmission 

1 μm 

300 THz 



Frequencies for Mobile Communication 

• VHF-/UHF-ranges for mobile radio 

– simple, small antenna for cars 

– deterministic propagation characteristics, reliable 

connections 

• SHF and higher for directed radio links, satellite 

communication 

– small antenna, focusing 

– large bandwidth available 

• Wireless LANs use frequencies in UHF to SHF spectrum 

– some systems planned up to EHF 

– limitations due to absorption by water and oxygen 

molecules (resonance frequencies) 

• weather dependent fading, signal loss caused by heavy 

rainfall etc. 

- 25 - 



Frequency Regulations 

• Frequency assignments are managed by the International 

Telecommunication Union – 

Radiocommuncation Sector (ITU-R) 

– holds auctions for new frequencies, manages frequency 

bands worldwide (WRC, World Radio Conferences) 

• National regulation authorities 

– Germany: Bundesnetzagentur (Federal Network Agency) 

– USA: Federal Communications Commission (FCC) 

- 26 - 



Important Frequency Assignments 

Cellular 

Phones 

Cordless 

Phones 

Wireless 

LANs 

Europe USA Japan 

GSM 450-457, 479- 

486/460-467,489- 

496, 890-915/935- 

960, 

1710-1785/1805- 

1880 

UMTS (FDD) 1920- 

1980, 2110-2190 

UMTS (TDD) 1900- 

1920, 2020-2025 

CT1+ 885-887, 930- 

932 

CT2 

864-868 

DECT 

1880-1900 

IEEE 802.11 

2400-2483 

HIPERLAN 2 

5150-5350, 5470- 

5725 

Others RF-Control 

27, 128, 418, 433, 

868 

AMPS, TDMA, CDMA 

824-849, 

869-894 

TDMA, CDMA, GSM 

1850-1910, 

1930-1990 

PACS 1850-1910, 1930- 

1990 

PACS-UB 1910-1930 

902-928 

IEEE 802.11 

2400-2483 

5150-5350, 5725-5825 

RF-Control 

315, 915 

- 27 - 

PDC 

810-826, 

940-956, 

1429-1465, 

1477-1513 

PHS 

1895-1918 

JCT 

254-380 

IEEE 802.11 

2471-2497 

5150-5250 

RF-Control 

426, 868 



ISM Bands: General facts 

Industrial, scientific, and medical (ISM) radio bands 

• originally reserved internationally by ITU-R for noncommercial 

use of RF electromagnetic fields for 

industrial, scientific and medical purposes 

• Individual countries' use may differ due to variations in 

national radio regulations 

• In recent years permission for license-free short-range 

communication applications such as walkie-talkies, 

remote controls, Wireless LANs, Bluetooth 

Source: Wikipedia 

- 28 - 



ISM Bands: Assignments 

Some typical ISM bands 

Frequency Comment 

13.553-13.567 MHz 

26.957-27.28 MHz 

40.66-40.70 MHz 

433-434 MHz Europe 

900-928 MHz America 

2.4-2.5 GHz WLAN/WPAN 

5.725-5.875 GHz WLAN 

24-24.25 GHz 

- 29 - 



Signal Propagation 

● Propagation in free space always like light (straight line) 

● Receiving power in free space proportional to 1/d² 

(d = distance between sender and receiver) 

● Sources of distortion 

● Reflection/refraction – bounce of a surface; enter material 

● Scattering – multiple reflections at rough surfaces 

● Diffraction – start “new wave” from a sharp edge 

● Doppler fading – shift in frequencies (loss of center) 

● Attenuation – energy is distributed to larger areas with 

increasing distance 

reflection refraction scattering diffraction 

- 30 - 



Attenuation results in path loss 

• Effect of attenuation: received signal strength is a 

function of the distance d between sender and 

transmitter 

• Captured by Frii's free-space equation 

– Describes signal strength at distance d relative 

to some reference distance d 0 < d for which 

strength is known 

– d 0 is far-field distance, depends on antenna 

technology 

- 31 - 



Pathloss in Free Space 

• Received power depends on frequency, 

transmitted power, antenna gains, distance and 

constants only 

P 

L 

L 

F 

R 

= 

P 

T 

⎛ 

⎜ 

⎝ 

λ 

4πd 

⎞ 

⎟ 

⎠ 

• EIRP: effective isotropic radiated power: 

– EIRP = P T G T 

2 

P 

( dB) 

= 10log 

P 

( dB) 

= 10log 

G 

R 

T 

G 

T 

T 

G 

R 

F f : Frequency [Hz] 

+ 10logG 

R 

- 32 - 

P 

G 

λ 

: 

d 

T / R 

T / R 

: 

: 

− 20log 

transmitted 

: Antenna Gain Transmitter/Receiver 

Wavelength[m] 

Distance[m] 

f 

/ received 

− 20log 

d 

Power 

+ 147. 

56 



Attenuation of different frequencies 

● Attenuation depends on the 

used frequency 

● Can result in a 

frequency-selective channel 

― If bandwidth spans 

frequency ranges with 

different attenuation 

properties 

Attenuation 

- 33 - 

moderate rain 

fog / clouds 

strong rain 

molecular dispersion 

frequency 



Atmospheric attenuation 

(dB/km) 

10 

1 

0.1 

0.01 

Attenuation in Atmosphere 

10 20 40 60 80 100 300 f (GHz) 

- 34 - 

vapor 

oxygen 

David Benkner: 

Digitale Mobilfunksysteme 



• Signal can take many different paths between sender and 

receiver due to reflection, scattering, diffraction 

signal at sender 

Multipath Propagation 

• Time dispersion: signal is dispersed over time 

interference with “neighbor” symbols, Inter Symbol 

Interference (ISI) 

• The signal reaches a receiver directly and phase shifted 

distorted signal depending on the phases of the different parts 

- 35 - 

LOS pulses multipath 

pulses 

signal at receiver 



Channel characteristics change over time and location 

– signal paths change 

– different delay variations of different signal parts 

– different phases of signal parts 

quick changes in the power received (short term/fast 

fading) 

Additional changes in 

Multipath Propagation 

– distance to sender 

– obstacles further away 

slow changes in the average power 

received (long term/slow fading) 

All fading effects are frequency-dependent 

- 36 - 

power 

short term fading 

long term 

fading 


Andreas Könsgen – Summer Term 2011 

t

Radio Channel Characteristics 

• Superposition of 

numerous direct and 

reflected multipath 

components with 

different attenuation 

and phasing 

• time variant 

• Differentiation of fast 

and slow fading 

• Fast fading due to superposition of different phases 

• Slow fading is due to the change of propagation 

environment 

• Both fading types depend on the frequency 

A 

- 37 - 

B 



Real World Example: Propagation 

- 38 - 



Real World Example: Time variation 

Signal 

amplitude 

5.18 

Frequency (GHz) 

Carrier frequency: 5.2 GHz 

Channel bandwidth: 40 MHz 

5.22 

- 39 - 

0 

0.5 

time (s) 

1 



Real World Example: Path Loss 

• Received power of 

a sender is 

decreasing with the 

distance between 

sender and 

receiver 

• Depends on 

Frequency 

• Many models, e.g. 

Okumura-Hata 

Walfish-Ikegami 

UMTS 30.03 

• Mostly shown in dB 

(attenuation) 

Pathloss [dB] 

40 60 80 100 120 140 160 

0 200 400 600 800 1000 

- 40 - 

Distance [m] 

UMTS 30.03 Vehicular 

From Walke: UMTS - the fundamentals 



Noise and Interference 

• So far: only a single transmitter assumed 

– Only disturbance: self-interference of a signal with multipath 

“copies” of itself 

• In reality, two further disturbances 

– Noise – due to effects in receiver electronics, depends 

on temperature 

• Typical model: an additive Gaussian variable, mean 0, no 

correlation in time 

– Interference from third parties 

• Co-channel interference: another sender uses the same 

spectrum 

• Adjacent-channel interference: another sender uses some 

other part of the radio spectrum, but receiver filters are not 

good enough to fully suppress it 

• Effect: Received signal is distorted by channel, corrupted by 

noise and interference 

- 41 - 



Channel models 

• Simplest model: assume transmission power and 

attenuation are constant, noise an uncorrelated Gaussian 

variable 

– Additive White Gaussian Noise model 

• Situation with no line-of-sight path, but many indirect 

paths: Amplitude of resulting signal has a Rayleigh 

distribution (Rayleigh fading) 

• One dominant line-of-sight plus many indirect paths: 

Signal has a Rice distribution (Rice fading) 

• Raytracing model 

– Given location of transmitters, receivers, obstacles 

– Calculate current SINR for each transmission path 

- 42 -

New Standards for Wireless LANs

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